import java.util.ArrayList;
import java.util.LinkedList;
import java.util.List;
import java.util.Queue;

public class BinaryTree {

    static class TreeNode {
        public char val;
        public TreeNode left;//左节点的引用
        public TreeNode right;//右节点的引用

        public TreeNode(char val) {
            this.val = val;
        }
    }

    //public TreeNode root;//根节点

    public TreeNode createTree() {
        TreeNode A = new TreeNode('A');
        TreeNode B = new TreeNode('B');
        TreeNode C = new TreeNode('C');
        TreeNode D = new TreeNode('D');
        TreeNode E = new TreeNode('E');
        TreeNode F = new TreeNode('F');
        TreeNode G = new TreeNode('G');
        TreeNode H = new TreeNode('H');

        A.left = B;
        A.right = C;
        B.left = D;
        B.right = E;
        C.left = F;
        C.right = G;
        E.right = H;

        return A;
    }

    // 前序遍历
    void preOrder(TreeNode root) {
        if (root == null) {
            return;
        }
        System.out.print(root.val + " ");
        preOrder(root.left);
        preOrder(root.right);
    }

//    List<Character> ret = new ArrayList<>();
//    public List<Character> preorderTraversal(TreeNode root) {
//        if (root == null) {
//            return ret;
//        }
//        ret.add(root.val);
//        preorderTraversal(root.left);
//        preorderTraversal(root.right);
//        return ret;
//    }

    public List<Character> preorderTraversal(TreeNode root) {
        List<Character> ret = new ArrayList<>();
        if (root == null) {
            return ret;
        }
        ret.add(root.val);

        List<Character> leftTree = preorderTraversal(root.left);
        ret.addAll(leftTree);
        List<Character> rightTree = preorderTraversal(root.right);
        ret.addAll(rightTree);

        return ret;
    }

    // 中序遍历
    void inOrder(TreeNode root) {
        if (root == null) {
            return;
        }
        inOrder(root.left);
        System.out.print(root.val + " ");
        inOrder(root.right);
    }

    // 后序遍历
    void postOrde(TreeNode root) {
        if (root == null) {
            return;
        }
        postOrde(root.left);
        postOrde(root.right);
        System.out.print(root.val + " ");
    }

    // 获取树中节点的个数
    public static int nodeSize = 0;
    void size(TreeNode root) {
        if (root == null) {
            return;
        }
        nodeSize++;
        size(root.left);
        size(root.right);
    }

    int size2(TreeNode root) {
        if (root == null) {
            return 0;
        }
        return size2(root.left) + size2(root.right) + 1;
    }

    // 获取叶子节点的个数
    public static int leafSize = 0;
    void getLeafNodeCount1(TreeNode root) {
        if (root == null) {
            return;
        }
        if (root.left == null && root.right == null) {
            leafSize++;
        }
        getLeafNodeCount1(root.left);
        getLeafNodeCount1(root.right);
    }

    int getLeafNodeCount2(TreeNode root) {
        int leafSize2 = 0;
        if (root == null) {
            return 0;
        }
        if (root.left == null && root.right == null) {
            return 1;
        }
        return getLeafNodeCount2(root.left) + getLeafNodeCount2(root.right);
    }

    // 子问题思路-求叶子结点个数
    // 获取第K层节点的个数
    int getKLevelNodeCount(TreeNode root, int k) {
        if (root == null) {
            return 0;
        }

        if (k == 1) {
            return 1;
        }

        return getKLevelNodeCount(root.left, k-1) +
                getKLevelNodeCount(root.right, k-1);
    }

    // 获取二叉树的高度
    int getHeight(TreeNode root) {
        if (root == null) {
            return 0;
        }
        int leftH = getHeight(root.left);
        int rightH = getHeight(root.right);
        return leftH > rightH ? leftH+1 : rightH+1;
    }

    // 检测值为value的元素是否存在
    TreeNode find(TreeNode root, int val) {
        if (root == null) {
            return null;
        }
        if (root.val == val) {
            return root;
        }

        TreeNode ret = find(root.left, val);
        if (ret != null) {
            return ret;
        }
        ret = find(root.right, val);
        if (ret != null) {
            return ret;
        }
        return null;
    }

    //层序遍历
    void levelOrder(TreeNode root) {
        if (root == null) {
            return;
        }
        Queue<TreeNode> queue = new LinkedList<>();
        queue.offer(root);

        while (!queue.isEmpty()) {
            TreeNode cur = queue.poll();
            System.out.print(cur.val + " ");
            if (cur.left != null) {
                queue.offer(cur.left);
            }
            if (cur.right != null) {
                queue.offer(cur.right);
            }
        }
    }

    public List<List<Character>> levelOrder2(TreeNode root) {
        List<List<Character>> ret = new ArrayList<>();
        if (root == null) {
            return null;
        }
        Queue<TreeNode> queue = new LinkedList<>();
        queue.offer(root);

        while (!queue.isEmpty()) {
            int size = queue.size();
            List<Character> list = new ArrayList<>();
            while (size != 0) {
                TreeNode cur = queue.poll();
                list.add(cur.val);
                size--;
                if (cur.left != null) {
                    queue.offer(cur.left);
                }
                if (cur.right != null) {
                    queue.offer(cur.right);
                }
            }
            ret.add(list);
        }
        return ret;
    }

    // 判断一棵树是不是完全二叉树
    boolean isCompleteTree(TreeNode root) {
        return false;
    }

}
